McCabe will part company with the council on 16 September after three years as assistant director of customer focus, communications and consultation.
He will launch McCabe Associates on 19 September.
Since McCabe arrived at the council in 2002, it has become one of the fastest-improving authorities, making the move from a poor Comprehensive Performance Assessment rating to good.
'We introduced a reputational strategy to make sure that people understood the concept of best value,' said McCabe.
The 15-strong comms team provides media relations, internal communications, publications including a bi-monthly residents magazine and consultation, and pro-active campaigns.
The biggest challenge for the next comms chief will be to continue with the improvement scheme and carry out effective consultation to the residents on the council's huge ten-year regeneration programme, said McCabe.
Islington's A1 borough project aims to regenerate Archway, Holloway Road and the Finsbury areas of north London.
'We have a diverse community, and effective consultation will play a key role in making the regeneration project a success,' he added.